1. Field of the Invention
The present invention relates to an acceleration control device for use in a motor vehicle equipped with an internal combustion engine for driving the motor vehicle. The present invention relates to a control system provided in a path for converting an amount of operation of an accelerator pedal operated by a driver of a motor vehicle into an electric signal and transmitting the electric signal to an actuator for controlling an opening of an accelerator of an engine and including a program control circuit. The present invention relates to a device, which can be utilized in various engines utilizing liquid fuels although it was developed for a motor vehicle equipped with a diesel engine. The present invention relates to an improvement of an auto-cruise device. The present invention relates to an improvement of fuel consumption and an improvement of engine exhaust gas.
2. Description of Related Art
An auto-cruise device for a motor vehicle is very popular nowadays. The auto-cruise device is generally defined as an automatic control device, a control of which is activated by a switching operation of a driver of the motor vehicle. A running speed of the motor vehicle is set as an aimed constant vehicle speed by the automatic control device at a time when the switching operation is performed by the driver. An accelerator opening of an engine of the motor vehicle is automatically controlled by the automatic control device such that the running speed of the vehicle is continuously maintained at an aimed constant speed. When such auto-cruise device is effectively operating, it is possible to run the motor vehicle at the constant speed even when an accelerator pedal of the motor vehicle is released. Such auto-cruise device has been widely utilized for a long distance cruise and/or a constant speed cruise of a motor vehicle.
It has been usual that a control of such conventional auto-cruise device can be released by a switching operation, a brake pedal operation or shift-down operation of a change gear by a driver of a motor vehicle. Further, such conventional auto-cruise devices is usually constructed in such a way that a motor vehicle can be accelerated overriding the control of the auto-cruise device when a driver steps on an accelerator pedal of a motor vehicle substantially in a state where the auto-cruise device is operating effectively. When a change switch capable of changing an aimed constant speed is provided in the operating switch circuit of the auto-cruise device, it is possible to accelerate or decelerate the motor vehicle by changing the aimed speed by means of the switch even if the driver's foot is separated from the accelerator pedal.
Further, it is usual for such conventional device that, when an aimed speed is changed by a driver's operation in a state where such auto-cruise device is operating effectively, an acceleration or deceleration control of a motor vehicle is executed such that the current running speed of the vehicle immediately reaches a new aimed speed. An example of such system is disclosed in JP2000-043611A (Matsuda). In the Matsuda invention, when an acceleration control or deceleration control of the motor vehicle running at a certain speed is performed, a control gain is changed according to the certain speed, as a result of which controllability is improved. That is, in the Matsuda invention, when an aimed speed is changed step by step under an automatic control, a feedback control or a feedforward control is utilized such that the running speed smoothly approaches a new aimed speed, that is, such that the so-called overshoot or control delay does not occur.
In the well known conventional auto-cruise device, the control thereby is activated by the driver as mentioned above and, so long as the present inventors know, there is no auto-cruise device, a control of which is automatically activated without requiring driver's operation when certain constant condition is established. Further, in the known auto-cruise device, a driver basically releases an accelerator pedal after the cruise control is activated as mentioned previously. However, although the conventional auto-cruise device in which a cruise control can be overridden after the cruise control is activated is known, there is no technical thought for changing a control function for controlling the accelerator opening of an engine, according to a depressing amount of an accelerator pedal, so long as the inventors of the present invention know.
Besides the auto-cruise device, it has been strongly requested by vehicle users to improve specific fuel consumption (distance covered by unit amount of fuel). Particularly, specific fuel consumption is one of very important factors when purchasers of commercial vehicles such as trucks or buses select vehicles. In addition, environmental contamination due to exhaust gas of vehicle engine has become a serious problem recently and possible measures on reduction of quantity of sulfur in diesel fuel are having been investigated by related surveying and research organizations. The reduction of sulfur content in diesel fuel requires additional diesel oil refining steps, causing-fuel cost to be increased. Therefore, it is presumed that the request for improvement of specific fuel consumption of vehicle is increased more and more.
In order to improve the specific fuel consumption effectively, the inventors of the present invention paid attention to the fact that one of various resistances occurring in a running vehicle, which require excessive fuel consumption, is an abrupt acceleration. That is, the resistances can be classified to an air resistance of a vehicle, a rolling frictional resistance of wheels thereof, an acceleration resistance and a gradient resistance, etc., and, when quantitative distribution of these resistances is considered, it is clear that a running resistance, which is controllable according to the running mode of vehicle, is the acceleration resistance. In order to reduce an influence of the acceleration resistance, it is preferable, to control an amount of fuel supply such that, when a new aimed vehicle speed is set, a practical vehicle speed approaches the new aimed vehicle speed gently and reasonably. In other words, it is effective to reasonably control an amount of fuel supply, which is used to generate an acceleration torque.
In the existing circumstances, such control may be realized by training drivers. That is, it is necessary to drum individual vehicle driver into the practice that, when a vehicle is to be accelerated, the driver must not ram an accelerator pedal but steps on it gradually and releases the pedal after a desired speed is achieved.
The inventions of the present invention had studied a possibility of realizing such practice, which is to be performed by individual driver, automatically by improving an auto-cruise device. That is, the present inventors had studied the possibility of controlling an amount of fuel supply to an internal combustion engine of a motor vehicle such that, when a driver rams an accelerator pedal of the vehicle in order to accelerate the vehicle, a reasonable acceleration is performed by not reflecting a depressing amount of the accelerator pedal directly to an amount of fuel supplied to the engine. This study is meaningless when a driver does not activate the conventional auto-cruise device in which the control is manually activated by the driver. On the other hand, a starting performance of the vehicle is degraded undesirably when an auto-cruise device is constructed such that a control of the auto-cruise device is automatically activated at an engine start time in a parking state and the control for gradually increasing an amount of fuel supplied to the engine is executed even if the driver rams the acceleration pedal as mentioned above.
As a result of the study, the present inventors had invented an acceleration control device, which is disclosed in JP2004-50904A. In the disclosed acceleration control device, an auto-cruise device is automatically activated when a constant vehicle speed is detected. In a state in which an auto-cruise control is effective, an aimed speed is incrementally set with small changing step even when the acceleration pedal is rammed, so that fuel supply is controlled such that a large amount fuel is not supplied at a time.
The present inventors have conducted various tests on the acceleration control device disclosed in JP2004-50904A and found that there are two matters thereof, which are to be improved.
The acceleration control device includes accelerator opening difference detection means for detecting a difference (Δ) in accelerator opening between a current vehicle speed and an aimed vehicle speed. The opening difference detection means includes a control map having an insensitive zone in a vicinity of Δ=0, at which a difference of accelerator opening detected by the difference detection means becomes constantly 0. The inventors of the present invention found that, although the insensitive zone functions appropriately when a vehicle with light load is running on a flat road, the insensitive zone may not work as intended by a driver when the vehicle is running with heavy load, for example, when the motor vehicle is running on an uphill road. That is, when the driver of a motor vehicle, which is running with heavy load, is aware of a speed down of the vehicle and steps on the accelerator pedal, it is empirically known that the vehicle does not respond to the depression of the accelerator pedal or barely responds thereto when the driver further steps on the accelerator pedal. Such phenomenon is inconvenient in a case where a motor vehicle is running on an ascending road, slope of which increases with increase of running distance. This is one of the matters to be improved.
Besides, this matter to be improved, the acceleration control device is constructed such that, when a motor vehicle running on a road passes another vehicle on the same road, the passing vehicle appropriately responds to the depression of the accelerator pedal. That is, a direction indicator is operated when the passing operation is performed. By utilizing the operation of the direction indicator, the acceleration control device is constructed such that the vehicle temporarily responds to the operation of the accelerator pedal during the passing operation. The acceleration control device is acceptable so long as the passing operation is concerned. However, when a usual road or a freeway along which the vehicle is running at a constant speed becomes an uphill road and a driver steps on the accelerator pedal to maintain the speed, there is a case where the vehicle does not respond to depression of the accelerator pedal. This is the other matter to be improved.